Radar, as an acronym for “radio detection and ranging”, is a wireless surveillance system which transmits electromagnetic waves in the high-frequency range (wavelength of 100 cm or less) to an object and receives electromagnetic waves reflected from the object to determine a distance to the object, direction, or altitude.
Radar initially has been used for military purposes such as search of a target, positioning, navigation, guidance, and bombing. Since its applicability has been extended through technological developments, radar currently has been used for the purpose of detecting the information relating to the altitude, speed, and position of an aircraft in aerospace engineering industry or determining the position of a ship and the position of an object in marine industry.
Also, recently, in line with the spread of an adaptive cruise control (ACC) technique for controlling a vehicle speed according to the speed of a vehicle ahead by sensing the vehicle ahead and a collision damage mitigation (CDM) technique for operating an automatic brake as well as giving an alarm to a driver when the collision between the vehicle ahead and the own vehicle is predicted, radar also has been used in automotive industry.
In line with the development of industries in which radar has been used as described above, radar is protected from the surrounding environment and moisture by mounting a radar cover on a front surface of the radar in order to effectively use the radar for an extended period of time. However, the radar cover mounted on the front surface of the radar causes electromagnetic wave loss due to the cover itself, and in particular, electromagnetic reflection loss on the surface of the radar cover may be very high.
Therefore, the radar cover must be made of a material capable of shielding transmitted electromagnetic waves at a predetermined level as well as having low electromagnetic reflection loss. That is, an electromagnetic wave shielding material having low reflection loss due to reflection as well as an appropriate electromagnetic wave shielding function may only be used as the radar cover.
However, in general, an electromagnetic wave shielding material, which is used in antenna manufacturing and reflectivity measurements, radar-tracking protection of aircrafts and ships, or absorption of electromagnetic waves of electronic devices, is a material capable of effectively reducing the intensity of electromagnetic waves by absorbing energy of the incident electromagnetic waves and converting their energy into heat using conduction, dielectric, and magnetic loss, i.e., a material with high penetration loss.
Thus, there is a need to develop a material for a radar cover which reduces the electromagnetic reflection loss and simultaneously does not inhibit radar signal transmission by controlling the shielding rate of the transmitted (penetrating) electromagnetic waves at an appropriate level.
Under the above-described background, while studying a material for a radar cover that protects a radar from the external environment and simultaneously does not inhibit radar signal transmission, the present inventors confirmed that a thermoplastic resin composition, in which carbon nanotubes and carbon black are added in optimal amounts and an optimal mixing weight ratio to a thermoplastic resin, has electromagnetic reflection loss and penetration loss characteristics to such a degree that does not inhibit radar signals while maintaining excellent mechanical properties, thereby leading to the completion of the present invention.